<!DOCTYPE html>
<html lang="en">
  <head>
    <meta charset="UTF-8" />
    <meta name="viewport" content="width=device-width, initial-scale=1.0" />
    <title>Document</title>
  </head>
  <body>
    <button>文档中的第一个按钮</button>
    <button>文档中的第二个按钮</button>
    <script>
      const btn = document.querySelector("button");
      console.log("选中第一个", btn);
      const btns = document.querySelectorAll("button");
      console.log("选中全部", btns);
      console.log(document);
      console.log(document.title);
      document.title = "修改后的标题";
      console.log(document.title);
      console.log(document.body);
    </script>
  </body>
</html>
